Pallet flow systems in which load-bearing pallets are caused to roll down an inclined track are in common use in warehouses and other materials handling operations. Typically, two rows of "skate wheels" are rotatably supported in two parallel steel channel shapes to provide an inclined track having a grade that is usually about 3 or 4 per cent, along which the pallets loaded with merchandise or other goods roll under the influence of gravity.
The pallet commonly has metal runners on its underside, together with a formed ridge to guide the pallet on a straight path as it flows down the inclined track, which is typically 20' to 100' or even more in length. Each pallet may carry a load of merchandise weighing as much as 3,000 pounds or more, so it is essential that a device or mechanism be provided for retarding the descent of each pallet down the long inclined track in order that the pallet will not pick up too much speed for safe operation.
Since some loads are very large, the retarding action provided by the retarder device or mechanism must be positive and reliable. In addition, since the load on the pallet can range from a very rigid container to poorly packaged, fragile materials, the retarding action must be gradual, with minimal shock to the load carried by the pallet.
Several retarder devices utilizing gear trains to control the speed of moving objects are known. Typically, the gear train terminates with a brake that is centrifugally actuated by rotation of the last rotatable member of the gear train. A common form of brake in this type of retarder device includes brake shoes that are directed radially outward by centrifugal forces to bear against a fixed brake drum. These drum types of retarder devices are not as efficient as would be desired, and generally do not provide for as smooth or gradual application of braking force as is desirable.